The wiring of electrical devices requires that electrical cables be inserted through openings or holes in junction boxes, panel boxes and the like. Electrical codes generally require that such access holes be substantially filled after insertion of electrical cable and the some means be provided to inhibit retraction of the electrical cable from the access hole after installation to eliminate the possibility of accidental disconnection of the electrical connections internal to the panel box, junction box, etc. The most commonly used connector to provide such utility until recently has been a two-part device that permitted passage of the cabling through a circular collar that passed through the access hole and provided means for securing the cabling inside the circular collar and a lock nut or other means for, in turn, securing the collar to the access hole. Such devices are unwieldy and sometimes difficult to install, especially when space is limited, because of the number of parts involved and the need to apply screw drivers and wrenches to attain proper and secure attachment.
More recently, unitary plastic, strain relief, cable connector clamps, that include a self-locking mechanism as well as a cable retention system have been developed and found broader application. This type of cable clamp or connector is essentially tubular with a slit along one side to enable the connector to be squeezed for insertion into the access bole in the panel box, junction box, etc. It then resiliently returns to its original shape and is provided with protruding ribs to lock it into the opening.
It is common practice to include in the tubular portion of such connectors, clamping elements that resiliently deflect as the cable is inserted, with the free end of the clamping element biased against the cable sheath so as to engage the sheath and thereby prevent the cable from being readily withdrawn from the opening after insertion and installation.
One such device is described in U.S. Pat. No. 5,594,209 to Nattel et al issued Jan. 14, 1997. This patent suggests a connector, as just described, that includes an internal clamping element that has a clamping lip that is resiliently pressed against the cable to prevent its removal from the connector. The clamping lip is described as having a reduced thickness at its free end and including additional projections on the inner wall of the tubular housing, which additional projections have abutment faces perpendicular to the axis of the housing.
U.S. Pat. No. 4,970,350 to Harrington, issued Nov. 13, 1990 describes a similar such connector device comprising a housing having first and second open ends and an inner wall forming a channel extending through the housing for receiving a cable. A coupling means is mounted within the housing for urging the cable towards the inner wall and includes a flange, means for grippingly engaging the cable between the inner wall and the flange, and an elongated bracing pin for providing resistance to bending of the flange.
While both of the foregoing patented devices provide useful solutions to the stated problem of providing a simple to use cable connector, their design is not optimal since they rely largely on simple friction or the presence of a single sharp surface to inhibit “pullout” of the inserted cable. Although the devices described in the foregoing patents allege an ability to retain a wide range of cable diameters, the range of their utility is really quite limited because of their design.
A better arrangement would provide a serrated engagement surface for retaining the inserted cable. Such a design provides a more secure retention of the inserted cable. The use of such a serrated surface, if properly designed, has the additional benefit of being more readily adaptable to a larger variety of cable diameters without sacrificing cable retention capability. The manufacture of such a connector using conventional plastic molding techniques is, however, not simple and requires redesign of the connector to obtain the required serrated contact points in such a process.
U.S. Pat. No. 6,080,933 issued Jun. 27, 2000 in the name of Thomas J. Gretz for, “Snap in Cable Connector” describes a locking cable connector composed of three mating pieces that snap together and provide a connector for helically wound armored or metal clad electrical conductors. A spring steel adapter is used in conjunction with an electrical junction box to fix the location of the locking cable connector with respect to the junction box. The first piece of the snap in locking cable connector is a die cast member including at its inbound end a smooth outer cylindrical section having an outer diameter with flanges that accommodates a spring steel adapter. The second piece is a spring steel locking ring provided to receive a helically wound shielded cable that is inserted into the out end of the die cast member. The locking ring has outwardly directed tangs that allow insertion into the die cast member but restrict withdrawal thereof from the die cast member by virtue of apertures in the walls of the entry end of the die cast cylindrical member. The locking ring also has oppositely or outwardly directed tangs to receive the armored cable and to restrict its movement in the opposite or withdrawal direction.
The spring steel locking ring has a cut out section that permits slight compression so that the locking ring may be easily inserted into the die cast member. Once inserted, the locking ring is able to expand to the full inner diameter of the die cast member to provide a tight and secure fit.
While all such prior art connector devices provide useful solutions to the problem of connecting armored or other cable to electrical boxes of one type or another, they are either relatively costly, if made of cast metal, or may lack adequate strength if molded from plastic. Accordingly, a simplified such connector device fabricated from stamped metal which demonstrates the strength of a cast fitting with a fabrication cost approaching that of a plastic such fitting would be highly desirable.